Charlize Theron 'didn't see' relationship with Sean Penn

The South African actress was surprised how her longstanding friendship with the actor and director blossomed into something more last year.

She told Vogue magazine: "What I guess I am trying to say is: A friend kind of stepped into that role [of boyfriend], and I really didn't see it coming.

"Sean and I have known each other for eighteen years. We were just really good friends. And it's been slow going because you are aware that you could screw that up and lose it.

"It just kind of naturally happened, and before I knew it, I was in something that was making my life better."

However, the 38-year-old star - who was previously in a relationship with the actor Stuart Townsend for nine years until 2010 - warns she's not interested in getting married anytime soon.

She added: "I really do understand the importance and what that ceremony represents to so many people, but it's just such a personal thing.

"Let's put it this way - I never had the dream of the white dress. And watching other people getting married? I think it's beautiful for them, but ... it's supposed to be this night of celebrating love, and all you see is a couple separated all night making sure everybody else is OK. And as you get older, you start sifting through the stuff that really matters."